MDLog: don't change expire_pos or read_pos on replay.
MDLog: don't change expire_pos or read_pos on replay.

These are unnecessary or rendered irrelevant by previous commit
removing read_pos from the on-disk Header.

Signed-off-by: Greg Farnum <7c97bbd3e62ab6303ee1daebcbc2d9d58823df1a@hq.newdream.net>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph